Expression of genes encoding neuropeptides and enzymes in the brain, with emphasis on the hypothalamus, are being studied. We have isolated the rat oxytocin gene and are continuing our transgenic mice experiments (that enabled expression of oxytocin in a tissue and physiologically specific fashion) with promoter-mutated transgenes. Several lines are being bred to homozygosity now to study physiological regulation of the transgenes in comparison with the endogenous counterpart. We have also been analyzing sites of action of vasopressin and oxytocin, both centrally and peripherally and during development, by in situ hybridization with probes for their receptors. We demonstrated that a diurnal rhythm in vasopressin receptor expression in the suprachiasmatic nucleus is not dependent on its ligand. We are also studying the novel POU protein, RHS2 (Brain-4), whose full- length cDNA we previously cloned. We have mapped the sites of expression, including during development in the mouse, of the four class Ill POU proteins t& further our understanding of their roles. We have also determined that the Brain-4 has recognition sites for autoregulation and are continuing our efforts to "knock-out" the gene through homologous recombination. Mapping of gene expression in the human hypothalamus continues: analyses of vasopressin and oxytocin, as well as of LHRH, have been submitted for publication. Maps of the opioids are completed and of the tachykinins, corticotropin-releasing factor, somatostatin, and growth hormone- releasing factor are in progress.